The present invention relates to a ram boring implement having a pneumatically driven percussion piston, which is movable in the axial direction in a reciprocating manner in a housing, a control sleeve, which is axially adjustable for reversing the direction of motion of the ram boring implement and is acted upon by the pressure in one of the pressure chambers formed on both sides of the percussion piston, and a spindle drive with which the control sleeve can be adjusted by turning a compressed air supply hose. Ram boring implements of this type are used for driving earth bores for cables and the like that are laid underground.
German Pat. No. 1,634,417 discloses a ram boring implement of this generic type. The percussion piston has a tubular section displaceable on the control sleeve and, in the peripheral wall of this tubular section, is provided with radial channels which are periodically opened and closed by the control sleeve during the oscillating motion of the percussion piston. The compressed air feed to the pressure chamber for driving the percussion piston is controlled in this way. If the control sleeve is located in a front position, the percussion piston, during its forward stroke, strikes against the front end of the housing so that impulse is transmitted to the housing and the ram boring implement is driven in the forward direction. If the control sleeve is located in the rear position, the motion of the percussion piston is pneumatically braked during the forward stroke before the percussion piston reaches the front end of the housing. Instead, the percussion piston in this case strikes against the rear end of the housing during its rearward stroke, so that the ram boring implement moves in the rearward direction.
In the conventional implement, the control sleeve is rigidly connected to the compressed air supply hose. The spindle drive for adjusting the control sleeve is formed by an external thread which is made on the control sleeve and is engaged with a component rigidly connected to the housing.
The pressure chamber located on the rearside of the percussion piston is made in the tubular section of the percussion piston and is defined toward the rear by the control sleeve made in a pot shape. When this pressure chamber is pressurized during the forward stroke of the percussion piston, a relatively large force directed toward the rear therefore acts on the control sleeve. For this reason, changing over from the rearward motion to the forward motion by axially adjusting the control sleeve forward can only take place when the compressed air feed is switched off. The thread of the spindle drive may only have a small pitch in order that the relatively large axial forces can be reliably absorbed. When the direction of motion of the ram boring implement is to be reversed and the compressed air hose is turned manually for this purpose, the compressed air hose must execute a large number of revolutions, as a result of which the reversal of the direction of motion is relatively laborious and time-consuming.